Exhaust gas recirculation (EGR) is used to reduce emissions and increase fuel economy in internal combustion engines. Exhaust gas is forced from the engine cylinders into the exhaust manifold after combustion. The exhaust gas includes non-burnable gas and other emissions that are otherwise released into the environment. Conventionally, EGR is used while the engine is running to reduce emissions and increase fuel economy.
The exhaust gas is mixed with intake air before entering the engine cylinders. Because the exhaust gas is non-burnable and takes up volume, the throttle has to open further in order to maintain a desired power level. A larger throttle opening reduces pumping losses and increases engine fuel efficiency.